Tag: neutron star

A warm Summer day. I’m under a shady tree by the lake, watching the geese and doing some math on Old Reliable. Suddenly a text-message window opens up on its screen. The header bar says 710-555-1701. Old Reliable has never held a messaging app, that’s not what I use it for. The whole thing doesn’t add up. I type in, Hello?

Hello, Mr Moire. Remember me?

Suddenly I do. That sultry knowing stare, those pointed ears. It’s been a year. Hello, Ms Baird. What can I do for you?

Another tip for you, Mr Moire. One of my favorite star systems — the view as you approach it at near-lightspeed is so ... meaningful. Your astronomers call it PSR J0337+1715.

So of course I head over to Al’s coffee shop after erasing everything but that astronomical designation. As I hoped, Cathleen and a few of her astronomy students are on their mid-morning break. Cathleen winces a little when she sees me coming. “Now what, Sy? You’re going to ask about blazars and neutrinos?”

I show her Old Reliable’s screen. “Afraid not, Cathleen, I’ll have to save that for later. I just got a message about this star system. Recognize it?”

“Why, Sy, is that a clue or something? And why is the lettering in orange?”

“Long story. But what can you tell me about this star system?”

“Well, it’s probably one of the most compact multi-component systems we’re ever going to run across. You know what compact objects are?”

“Sure. When a star the size of our Sun exhausts most of its hydrogen fuel, gravity wins its battle against heat. The star collapses down to a white dwarf, a Sun-full of mass packed into a planet-size body. If the star’s a bit bigger it collapses even further, down to a neutron star just a few miles across. The next step would be a black hole, but that’s not really a star, is it?”

“No, it’s not. Jim, why not?”

“Because by definition a black hole doesn’t emit light. A black hole’s accretion disk or polar jets might, but not the object itself.”

“Mm-hm. Sy, your ‘object’ is actually three compact objects orbiting around each other. There’s a neutron star with a white dwarf going around it, and another white dwarf swinging around the pair of them. Vivian, does that sound familiar?”

“That’s a three-body system, like the Moon going around the Earth and both going around the Sun. Mmm, except really both white dwarfs would go around the neutron star because it’s heaviest and we can calculate the motion like we do the Solar System.”

“Not quite. We can treat the Sun as motionless because it has 99% of the mass. J0337+1715’s neutron star doesn’t dominate its system as much as the Sun does ours. That outermost dwarf has 20% of its system’s mass. Phil, what does that suggest to you?”

“It’d be like Pluto and Charon. Charon’s got 10% of their combined mass and so Pluto and Charon both orbit a point 10% of the way out from Pluto. From Earth we see Pluto wobbling side to side around that point. So the neutron star must wobble around the point 20% outward towards the heavy dwarf. Hey, star-wobble is how we find exoplanets. Is that what this is about, Mr Moire? Did someone measure its red-shift behavior?”Cathleen saves me from answering. “Not quite. The study Sy’s chasing is actually a cute variation on red-shift measurements. That ‘PSR‘ designation means the neutron star is a pulsar. Those things emit electromagnetic radiation pulses with astounding precision, generally regular within a few dozen nanoseconds. If we receive slowed-down pulses then the object’s going away; sped-up and it’s approaching, just like with red-shifting. The researchers derived orbital parameters for all three bodies from the between-pulse durations. The heavy dwarf is 200 times further out than the light one, for instance. Not an easy experiment, but it yielded an important result.”

My ears perk up. “Which was…?”

“The gravitational force between the pulsar and each dwarf was within six parts per million of what Newton’s Laws prescribe. That observation rules out whole classes of theories that tried to explain galaxies and galaxy clusters without invoking dark matter.”

“Sometimes right, often wrong. Thing was, he generated too many ideas for people to cope with. Worse, he was one of those wide-ranging intellects who adds one plus one to make two. Trouble was, Zwicky got his ones from different specialties that don’t normally interact. When people didn’t immediately run with one of his claims he took it personally and lashed out, publicly called ’em fools or worse. Never a good tactic.”

“Gimme a f’rinstance.”

“OK. Early 1930’s, Zwicky’s out in the still-raw wilds of California, practically nothing out there but movie studios and oil wells, using a manual blink-comparator like the one Clyde Tombaugh used about the same time to find Pluto. He’s scanning images taken with Palomar’s new wide-angle telescope to search out novae, stars that suddenly get brighter. He’s finding dozens of them but a few somehow get orders of magnitude brighter than the rest. He and his buddy Walter Baade call the special ones ‘supernovae.'”

“Ain’t that novas?”

“Novae — we’re being proper astronomers here and it’s a Latin word. Anyway, Zwiky’s trying to figure out where a supernova’s enormous luminosity comes from. He got his start in solid-state physics and he still keeps up on both Physics and Astronomy. Just a year earlier, James Cavendish over in atomic physics had announced the discovery of the neutron. Zwicky sees that neutrons are the solution to his problem — gravity can pack together no-charge neutrons to a much higher density than it can pack positive-charge protons. He proposes that a supernova happens when a big-enough star uses up its fuel and collapses to the smallest possible object, a neutron star. Furthermore, he says that the collapse releases so much gravitational energy that supernovae give off cosmic rays, the super-high-energy photons that were one of the Big Questions of the day.”

“Sounds reasonable, I suppose.”

“Well, yeah, now. But back then most astronomers had never heard of neutrons. To solve at a stroke both cosmic rays and supernovae, using this weird new thing called a neutron, and with the proposal coming from somewhere other than Europe or Ivy League academia — well, it was all too outlandish to take seriously. No-one did, for decades.”

“He didn’t like that, huh?”

“No, he did not. And he railed about it, not only in private conversations but in papers and in the preface to one of the two galaxy catalogs he published. Same thing with galaxy clusters.”

“I did and she did. Actually, I wrote that she confirmed clustering. We knew for 150 years that galaxies bunch together in our 2-D sky, but it took Zwicky’s measurements to group the Coma Cluster galaxies in 3-D. Problem was, they were moving too fast. If star gravity were the only thing holding them together they should have scattered ages ago.”

“Dark matter, huh?”

“Yup, Zwicky claimed invisible extra mass bound the cluster together. More Zwicky outlandishness and once again his work was ignored for years.”

“Even though he was right.”

“Mm-hm. But he could be wrong, too. He didn’t like Hubble’s expanding Universe idea so he came up with a ‘tired light’ theory to explain the red-shifts. He touted that idea heavily but there was too much evidence against it.”

“One of those angry ‘lone wolf’ scientists.”

“And bitter.”

~~ Rich Olcott

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